1,721,097 research outputs found
What is the Future of Two-Stroke S.I. Engine?
No full textThe scavenging process of two-stroke engines is unfavourably characterised by the loss of large part of the fresh charge from the exhaust port. Besides, bad combustion and misfire occur at light loads, because of the excessive ratio of residual gas to fresh gas within the cylinder. To avoid fuel short-circuiting to the exhaust port, the solution is direct fuel injection, as well as charge stratification or ATAC are the solutions for light-load operation.
With direct fuel injection and charge stratification or ATAC, the simple two-stroke engine with loop-and-crankcase scavenging for motorbikes, thanks to its intrinsic internal EGR, might satisfy the ECE 2002 exhaust emission limits even without catalytic converter.
Evolved two-stroke engines should be considered for application on automobiles, since direct injection and charge stratification equalise four-stroke and two-stroke-engines as regards exhaust emissions. Besides, two-stroke engines deliver higher torque, especially at low engine speeds and, of course, have double firing frequency that allows reducing the number of cylinders. In this case, two-stroke engines with poppet valves and external scavenging blower are preferable, to facilitate lubrication and to reduce oil consumption, engine wear and cylinder thermal deformation
Energy and Economic Comparison between natural gas fired and biomass fired Combined Heat and Power (CHP) plants for tissue paper production in remote areas
No full textIn remote areas, such as India, Africa and Southeast Asia, typically not connected to the natural gas distribution grid, tissue paper drying process is currently carried out using a Yankee cylinder, heated with saturated steam, and hot air hoods warmed with saturated steam or diathermic oil. In this way the drying impingement air is heated, at maximum, at around 250 °C, with consequent low levels of dried paper production in comparison to modern hoods heated with natural gas.
In this context, the present study intends to evaluate the technical and economic feasibility of using a CHP plant fully powered by biomass, for the production of steam and electricity in order to satisfy all the electrical needs of the paper mill and the steam for the Yankee cylinder, while a wood biomass fixed bed downdraft gasification plant is utilised for the production of syngas to be used as fuel in the gas hoods, in order to reach high drying temperatures (around 500 °C), comparable with those of the current natural gas powered hoods. Using previously developed calculation codes, an evaluation of the overall energy performances of the paper drying system and of the gasification plant has been performed.
Results show that, for a paper mill with a production of about 80 t/day of paper, two gasification reactors with a thermal output of about 1.95 MWt, and a consumption of dry biomass of 0.86 t/h, are required. For the steam system, the net electric power needed to meet the needs of the paper mill is about 3100 kW with a consumption of 4.72 t/h of moist biomass and a net efficiency of 23.9 %.
The performances of this innovative biomass fueled CHP plant are finally compared with those of a traditional natural gas fueled CHP plant
Analysis of the Behaviour of a 4-Stroke SI Engine Fuelled with Ammonia and Hydrogen
No full textThe use of hydrogen as fuel represents a possible solution to reduce greenhouse gas
emission from vehicles. Although proper engine running with hydrogen has been widely
demonstrated, hydrogen storage onboard of the vehicle is a major problem.
A promising solution is storing hydrogen in the form of ammonia that is liquid at
roughly 9 bar at environmental temperature and therefore involves relatively small
volumes and requires light and low-cost tanks.
Ammonia can be burned directly in IC engines, however a combustion promoter is
necessary to support combustion. As a matter of fact, the best (and carbon-free) promoter
is hydrogen, which has very high combustion velocity and wide flammability range,
whereas ammonia combustion is characterised by low flame speed and temperature,
narrow flammability range and high ignition energy.
The experimental activity shown in this paper is focused on analysing the behaviour of
a 4-stroke twin-cylinder SI engine of 505 cm3 fuelled ammonia-plus-hydrogen. This engine
was expressly chosen and modified to be placed in a range extended vehicle where
hydrogen is obtained from ammonia by means of on-board catalytic reforming. The
experimental results confirm that it is necessary to add hydrogen to air-ammonia mixture
to improve ignition and to increase combustion velocity, with ratios that depend mainly on
load and less on engine speed. Owing to intake air dilution and to lower flame speed of the
ammonia-hydrogen-air mixture, a general decrement in engine performances has been
detected in respect to the original gasoline version
Implementation of a novel hydrogen direct-injection concept in single and multi-cylinder engines: CFD, experimental and engine powertrain design studies
No full textA novel low-pressure hydrogen direct-injection system, characterised by low storage residual pressure and simple mechanical solutions, has been implemented in single and multi-cylinder engines. Based on two-step operation, this system keeps hydrogen metering apart from injection. The first step relates to the system with constant H2 flow rate and variable opening duration. The second step is characterised by variable H2 flow rate and constant angular duration. A prototype has been realised modifying a single-cylinder production engine, following the results of a wide CFD activity during which in-cylinder hydrogen injection and mixing phases have been simulated to investigate how valve and seat-valve geometries affect mixing characteristics. The prototype engine ran properly at full load, without pre-ignition, knocking or roughness even with stoichiometric or slightly rich mixtures, providing higher maximum power than with gasoline. At part load the engine worked correctly even with very lean mixtures. Current research is directed to explore the feasibility of applying the two-step injection concept in a multi-cylinder engine. The CFD analysis together with the design study aimed to integrate the injection system in the engine powertrain are shown and discussed
Sistema di iniezione diretta di idrogeno per motori ad A.C
No full textIl presente trovato realizza un sistema di iniezione diretta di idrogeno in fase gassosa per motori ad accensione comandata, il quale permette di non incorre negli inconvenienti sopra detti di sfruttamento solo parziale dell’idrogeno stoccato a bordo del veicolo e della necessità di iniettori di caratteristiche eccezionali. Infatti, grazie al fatto che l’iniezione dell’idrogeno nel cilindro motore avviene attraverso una valvola a fungo attuata meccanicamente, che permette un’ampia sezione di passaggio, è possibile iniettare considerevoli quantità di idrogeno in tempi ridotti utilizzando basse pressioni di iniezione (ad esempio 6 bar). A monte della valvola di iniezione è collocato un piccolo serbatoio all’interno del quale viene iniettata la voluta quantità di idrogeno attraverso un normale elettro-iniettore utilizzato su motori alimentati a gas naturale. La pressione di iniezione verso il piccolo serbatoio è tale da garantire sempre le condizioni di efflusso sonico attraverso l’elettro-iniettore, in modo da avere dipendenza lineare tra durata di iniezione e quantità d’idrogeno iniettata
Progress in Two-Stroke S.I. Engines
No full textThanks to its lightness, small dimensions and attractive simplicity, the two-stroke, S.I. engine may be potentially preferable to the four-stroke one for city cars and other small vehicles.
However, the loss of fresh mixture from the exhaust port, together with bad combustion and/or misfire at light loads constitute great limitations.
Our researches directed to solve these problems concern the development of an air-assisted, low-pressure, pumpless injection systems, which bypasses the trapping losses, and the solution of combustion problems at light loads by means of charge stratification and innovative ignition systems
Iniezione pneumatica a bassa pressione per motori a due tempi ad A.C. con pre-evaporazione del carburante
No full textVengono presentati i risultati sperimentali ottenuti adottando la pre-evaporazione del combustibile in un sistema di iniezione pneumatica “pumpless” a bassa pressione per motori a due tempi ad A.C., già ampiamente sperimentato (senza la pre-evaporazione) in precedenza e caratterizzato da una grande semplicità costruttiva, perché l’aria di iniezione viene fornita dal carter-pompa, che peraltro continua a svolgere anche il suo compito convenzionale di erogatore dell’aria di lavaggio
Sistema di iniezione diretta di idrogeno per motori ad A.C.
No full textIl presente trovato realizza un sistema di iniezione diretta di idrogeno in fase gassosa per motori ad accensione comandata, il quale permette di non incorre negli inconvenienti sopra detti di sfruttamento solo parziale dell’idrogeno stoccato a bordo del veicolo e della necessità di iniettori di caratteristiche eccezionali. Infatti, grazie al fatto che l’iniezione dell’idrogeno nel cilindro motore avviene attraverso una valvola a fungo attuata meccanicamente, che permette un’ampia sezione di passaggio, è possibile iniettare considerevoli quantità di idrogeno in tempi ridotti utilizzando basse pressioni di iniezione (ad esempio 6 bar). A monte della valvola di iniezione è collocato un piccolo serbatoio all’interno del quale viene iniettata la voluta quantità di idrogeno attraverso un normale elettro-iniettore utilizzato su motori alimentati a gas naturale. La pressione di iniezione verso il piccolo serbatoio è tale da garantire sempre le condizioni di efflusso sonico attraverso l’elettro-iniettore, in modo da avere dipendenza lineare tra durata di iniezione e quantità d’idrogeno iniettata
Numerical and Experimental Analysis on a Small GDI, Stratified Charge, Motorcycle Engine
No full textIn the field of engines for light motorcycles, two-stroke cycle survival is submitted to the application of direct fuel injection and charge stratification, even in the case of low-cost small engines. However, charge stratification is a difficult target in two-stroke engines, chiefly because timings of late injection (necessary for charge stratification) and of early injection (necessary for homogeneous charge) are much closer than in four-stroke engines. The compatibility between stratified and homogeneous charge operations needs a thorough CFD study of injection and mixing processes, with the support of techniques of spray visualization. Results strongly depend on the possibility of optimising the interaction between in-cylinder gas-dynamic field and spray; experimental activity is necessary as data source and verification of computational prediction. This paper shows the latest CFD investigation, experimental tests and results concerning a 50 cm3 engine for light motorcycles. The injection is of the liquid type with wall-and-air guided spray produced by a swirl injector. The research has been focused on the attainment of charge stratification at every engine speed. Spray actual characteristics have been investigated, attesting suitable repeatability and proper variation versus backpressure. Engine satisfactory behaviour even at light loads in unthrottled condition is proved by good fuel economy and engine stability in dynamometric bench tests. Exhaust gas analysis and indicated pressure behaviour confirm stratification and combustion correctness
Oxy-steam co-gasification of sewage sludge and woody biomass for bio-methane production: an experimental and numerical approach
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